In the automotive industry the hot blow forming of certain highly formable aluminum alloy sheet materials has been developed by the assignee of this invention for the forming of body panels and other parts of complex shape. In the case of superplastic AA5083 sheets, for example, such forming is often done between opposing heated tools that grip edges of a preheated sheet blank profile. One tool provides a forming surface on one side of the sheet material and the other tool provides a chamber on the other side of the sheet for application of a pressurized working gas to stretch the sheet against the forming surface. The pressurized gas, of course, applies a shaping force on the surface of the sheet.
It has been found in forming some product shapes that it would be useful to apply the force of a mechanical device to supplement the pressurized gas in stretching the sheet to shape the part. The mechanical device would be used inside the forming chamber but activated from outside the hot high pressure chamber during a stretch forming operation. In hot blow forming one to two millimeter thick AA5083 sheet material, for example, the temperature of the forming tools and sheet material is typically in the range of about 400° C. to 500° C. and air pressures of 100 to 200 psi and higher are employed. The outside mechanical actuator must be operatively connected with the internal forming device to seal against pressure and manage heat loss. It is an object of this invention to provide a mechanism or machine for such use in combination with heated and pressurized blow forming tools for sheet materials.